Aminoglycosides are potent bactericidal agents. Their main mechanism of action is on the bacterial ribosome, which in turn inhibits protein synthesis. They are active against a wide range of gram-positive and gram-negative species as well as mycobacteria. For some serious gram-negative infections, aminoglycosides or aminoglycosides in combination with other antimicrobials may be the drug of choice for Pseudonomas and other infections.
Lower respiratory tract infections with pseudomonas aeruginosa (Psa) are a major cause of morbidity and mortality among patients with cystic fibrosis (CF) and non-CF bronchiectasis. Once an infection is established, even aggressive antibiotic treatments may only temporarily reduce the number of Psa organisms in the respiratory tract. As a result, many CF patients have persistent Psa infections requiring frequent hospital admissions for intravenous chemotherapy.
Bronchiectasis is a condition characterized by progressive destruction and dilatation of airway walls due to infected retained secretions that result from a failure of airway defenses to maintain the sterile environment of the lower respiratory tract airways and lung parenchyma. The large volumes of infected secretions requiring aggressive antibiotic treatment at the onset of the infection and the presence of marked bacterial resistance to common and often used antibiotics represent significant barriers to effective therapy. The most effective treatment of bronchiectasis remains antibiotic therapy, usually administered systemically orally or by intravenous injection.
Aminoglycosides are considered one of the most useful classes of antibiotics for treating Psa infections. However, antibiotic therapy of a variety of respiratory infections, in particular bronchiectasis, continues to represent a major medical challenge.
One of the major disadvantages of aminoglycosides is that they can induce fairly severe side effects. Aminoglycosides are generally poorly absorbed orally and, for this reason, are given intravenously or intramuscularly. Aminoglycosides active against Psa penetrate into sputum poorly, making it necessary to administer large systemic doses intravenously in order to optimize sputum penetration at the site of infection in the lung. Such high doses can produce both nephrotic and ototoxic effects, often causing permanent renal insufficiency and auditory nerve damage, with deafness, dizziness, and unsteadiness.
At the same time, underdosing and incomplete courses of antibiotics are part of the problem of ineffective therapy. Potential consequences of underdosing respiratory tract infections include inadequate pathogen eradication, development of antibiotic resistance and lengthened eradication times, as well as potential for persistent clinical symptoms due to increasing lung injury, bronchiectasis, scarring, and premature death.
The overuse of antibiotics in the treatment of respiratory infections is a major problem and is increasingly regarded as such by both the medical community and the pharmaceutical industry. The Center for Disease Control (CDC) considers the growing problem of antibiotic resistance to be one of the most important public health challenges of our time. The CDC views overprescription of antibiotics as one of the prime culprits for the growing antibiotic resistance problem.
In view of the above problems in antibiotic therapies, research has primarily focused on the discovery of new molecules to provide possible solutions. Alternatively, the potential effectiveness of treating infections of the respiratory tract with aminoglycosides administered by new drug delivery technologies such as inhalation aerosols has been investigated. In particular, aerosolized antibiotics have been administered by small volume nebulizers (SVN) driven ultrasonically or by air compressors.
For two decades, inhaled antibiotics have been used effectively for ameliorating chronic pulmonary infections in conditions such as cystic fibrosis and non-CF bronchiectasis. To date, the U.S. Food and Drug Administration (FDA) has approved only one aerosolized antiinfective: TOBI® (Chiron Corporation, Seattle, Wash.). TOBI is a tobramycin solution for inhalation by nebulization. Tobramycin (O-3-amino-3-deoxy-α-D-glucopyranosyl-(1-4)-O-[2,6-diamino-2,3,6-trideoxy-α-D-ribo-hexopyranosyl-(1-6)]-2-deoxy-L-streptamine) is a water soluble, aminoglycoside antibiotic having a molceular weight of 467.52 g/mol. Tobramycin is effective against gram negative pathogens, in particular Pseudomonas aeruginosa, the key infective agent in CF patients.
The formulated TOBI product is an aqueous solution, which is sterile, clear, slightly yellow, non-pyrogenic, and is pH and salinity adjusted. It comprises 300 mg of tobramycin free base in 5 ml of sodium chloride (2.25 mg/ml) at pH 6.0 and is stable at 2-8 C. for two years, or 28 days at room temp. The solution darkens in intense light. At pH 6.0, approximately 2.2 of the 5 tobramycin amino groups have been converted to sulfate salts. A dose is a single 300 mg ampoule bid (12 hours apart).
Patients receive a 28 day “on” therapy followed by a 28 day “off” period, to reduce the potential for development of resistant bacterial strains. Of the 300 mg inhaled, only approximately 10% or 30 mg is delivered to the lung. Systemic tobramycin given by IV injection has serious adverse effects including renal and ototoxicity. High IV doses are typically given due to poor penetration of the drug across the lung endothelium and into sputum. Clinical studies with TOBI have shown that inhaled tobramycin may lead to tinitus and voice alteration.
Nebulization has many well documented disadvantages, including extended administration time, high cost, poor efficiency and reproducibility, risk of bacterial contamination, and the need for bulky compressors or gas cylinders. These disadvantages likely have an impact on patient compliance.
Pulmonary delivery by aerosol inhalation has received much attention as an attractive alternative to intravenous, intramuscular, and subcutaneous injection, since this approach eliminates the necessity for injection syringes and needles. Pulmonary delivery also limits irritation to the skin and body mucosa which are common side effects of transdermally, iontophoretically, and intranasally delivered drugs, eliminates the need for nasal and skin penetration enhancers (typical components of intranasal and transdermal systems that often cause skin irritation/dermatitis), is economically attractive, is amenable to patient self-administration, and is often preferred by patients over other alternative modes of administration. Administration of aminoglycoside dry powder aerosols to the lung has been attempted, but inefficient delivery devices and/or poorly dispersible lactose formulations limited these studies.
Dry powder inhalers are known in the art as disclosed, for example, in U.S. Pat. Nos. 5,458,135; 5,740,794; 5,775,320; and 5,785,049, and in copending U.S. application Ser. Nos. 09/004,558 filed Jan. 8, 1998, 09/312,434 filed Jun. 4, 1999, 60/136,518 filed May 28, 1999, and 60/141,793 filed Jun. 30, 1999, all of which are hereby incorporated in their entirety by reference.
In addition, U.S. Pat. No. 5,875,776 discloses a dry powder inhaler and discloses antibiotics such as gentamicin sulfate, amikacin sulfate, and tobramycin sulfate, among an extensive list of agents suitable for administration by the devices disclosed therein. No examples of formulations are disclosed. WO 00/35461 further discloses a method for treating bronchiectasis comprising the administration of an aminoglycoside aerosol.
A hollow porous tobramycin dry powder formulation was engineered and delivered from the Turbospin (PH&T, Italy) dry powder inhaler in a recent clinical study. Of the 25 mg of powder loaded into the capsule in the clinical study, only 4.6 mg (18.4%) of active drug substance was delivered to the lung. At this drug loading and efficiency, approximately 6 capsules (ca. 27.6 mg) are required to deliver a lung dose equivalent to the nebulized TOBI product. The requirement for administering at least 6 capsules raises issues with respect to patient compliance for such a therapy.
Despite the advances in discovering newer, broad spectrum antibiotics and drug delivery technologies, there remains a need for improved methods for administering antibiotics such as aminoglycosides. In particular, the maximum safe systemic dosages of aminoglycosides administered according to current therapies provide much less than the dose sufficient to achieve amounts of drug in lung tissue and secretions to exceed the minimum inhibitory capacity (i.e. concentrations capable of eliminating or significantly decreasing the bacterial burden causing the infection in the airways and lung tissues). Thus, therapy is likely to be inadequate while encouraging the emergence of resistant organisms and the development of adverse side effects. There remains a need for a patient-friendly means of administering aminoglycosides to patients which will provide higher localized concentrations of drug in the airway secretions and adjacent lung tissue without the risk of significant systemic side effects. Ideally, such administration must be from a device which is practical such that patient compliance is encouraged. The present invention meets these and other needs.